Background: One in ten women will undergo surgery for pelvic organ prolapse (POP) and/or urinary incontinence (1,31). Many others have symptoms or signs of pelvic floor dysfunction. Despite the large number of women affected by POP, there is a dearth of information needed to answer basic questions about the natural history of POP. The broad aim of the proposed study is to obtain a greater understanding of the natural history of POP. The specific aims of this study are to 1) describe the prevalence of and risk factors associated with POP, 2) describe the natural progression of POP by analyzing the incidence rate, annual rate of progression, and factors that influence the onset or progression of POP, and 3) describe the correlation between symptoms and signs in POP. Information gained will be used to determine the clinical significance of Stage 1 POP and to develop a definition for "clinically significant" POP. Study population: Women with intact uteri enrolled in the estrogen-replacement clinical trial arm of the Women s Health Initiative at the Iowa City, Iowa site. Study design: On four occasions at annual intervals, approximately 400 women will undergo a structured physical evaluation, incorporating the International Continence Society pelvic organ prolapse quantification system, and a screening symptom survey. Significance of this work: Pelvic organ prolapse affects the health of many American women. The population most likely to be affected by this disorder, older women, is steadily increasing. The national cost burden is large. This project will provide fundamental data to guide future decisions about intervention threshold, preventative measures, and risk factor modification.